Pressure-release structure for transducer



Oct. 1 1959 L. w. CAMP 2,908,245

PRESSURE-RELEASE STRUCTURE FOR TRANSDUCER Filed Dec. 50, 1957 IN VEN TOR.

LEO/V W. CAMP ATTORNEY 2,908,245 Patented Oct. 13, 19 59 ice A PRESSURE-RELEASE STRUCTURE FOR TRANSDUCER Leon W. Camp, Santa Monica, Calif., assignor to Bendix Aviation Corporation, North Hollywood, Calif., a corporation of Delaware Application December 30, 1957, Serial No. 706,069 6 Claims. (Cl. 116-137) This invention relates to sonic transducers for use in liquids and is particularly useful with, although not limited to, transducers for generating high-intensity sonic waves in liquids for cleaning purposes.

Itis often desirable to employ transducers of configuration having an intermediate or neck portion terminating in a head portion of larger lateral dimension, the outer end of the head portion constituting the working face from which useful energy is radiated into the liquid. However, the rear surfaces of those portions of the head projecting laterally beyond the neck portion also vibrate with substantially the same intensity as the face, and transmit undesired sonic energy into the liquid. This latter energy performs no useful function and is wasted. Furthermore, it may cause cavitation corrosion of the rear surfaces of the head itself and of surfaces back of the head. Of course, cavitation corrosion also results and is unavoidable at the working face, but this problem can be solved by providing a resistant, replaceable wear plate on the working face.

An object of the invention is to reduce the acoustic radiation from the rearwardly directed surfaces of a transducer and thereby conserve power and reduce cavitation corrosion.

A feature of the invention is a pressure-release body positioned in contact with or close to a vibrating surface of a liquid-immersed transducer from which transfer of sonic energy to the liquid is to be suppressed.

Other more specific objects and features of the invention will appear from the description to follow.

Heretofore, the only known practicable method of reducing acoustic coupling between a vibrating surface of a transducer and a liquid in which it is immersed was to separate the surface from the liquid by a coating of pressure-release material such as air cell rubber, plastic, or the like. Difiiculties have been encountered in maintaining such coatings intact on surfaces vibrating at high intensity.

The present invention is based on the principle that pressure waves in liquids can be efiiciently generated by a vibrating face in contact therewith only when free movement of the liquid adjacent the surface is restricted by the mass of a body of liquid of substantial size (measured in terms of wavelength). Otherwise, the liquid adjacent the vibrating surface moves freely with the surface without the generation of appreciable pressure therein. In accordance with the invention, this principle is used to reduce acoustic loading of and cavitation corrosion of a submerged surface by positioning a readily compressible body in the liquid close to, but not necessarily in contact with, the surface. In practice, the body may be an airfilled flexible container. Since the invention does not depend for its effectiveness on adhesion of the body to the transducer surface, it is effective over a longer period of time than the pressure-release coatings of the prior art.

A full understanding of the invention may be had from the following detailed description with reference to the drawing, in which:

high pressure waves generated therein.

Fig. 1 is an end view of a transducer incorporating the invention. v

Fig. 2 is a side elevational view of the transducer assembly of Fig. 1.

Fig. 3 is a partial longitudinal section taken in the plane III-III of Fig. l.

Fig. 4 is a side elevational view showing a modified form of the invention.

The drawing shows the invention applied to a transducer 10 of the type disclosed in copending application of L. W. Camp and I. P. ONeill Serial No. 687,725, filed October 2, 1957. Briefly, the transducer comprises a magnetostriction driver 10a joined to a motion amplifier 10b, the outer end 11 of which constitutesthe working face for generating desired sonic waves in a liquid in which it is submerged. The liquid is contained in a tank, only a portion of the wall 12 of which is shown. The motion amplified is cylindrical through most of its length and extends through an orifice 12a in the tank wall 12, being sealed by an O -ring 13, and restricted as to longitudinal movement by a flange 14 inside of the orifice and a snap ring 15 outside of the orifice.

The outer end portion of the motion amplifier is constituted by a head 16 which merges from circular crosssection at its joinder to the cylindrical section, hereinafter sometimes referred to as the neck portion, to square cross-section at the face 11. This transition in crosssectional shape results in overhanging lips 17 which project substantially from the neck portion of the transducer at the diagonals or corners of the square face 11. The rearwardly directed or facing portions of the overhanging lips 17 vibrate substantially in unison with the face 11, and generate powerful pressure waves in the liquid if nothing is done to prevent it. Such waves are directed rearwardly and may produce cavitation corrosion on any portion of the structure rearwardly of-the face, in addition to cavita-. tion corrosion of the surfaces 17 themselves.

In accordance with the present invention, a toroid 18 of flexible material, such as rubber or plastic material, is positioned against the head 16 adjacent its joinder to the neck portion therebelow. The diameter of the toroid is such, with respect to the lateral dimensions of the head 16, that the toroid cannot escape from the head, but bears thereagainst. In many installations, the transducers 10 are mounted vertically as shown in the drawing. Under such circumstances, the buoyancy of the toroid is sufiicient to maintain it is position resting against the under side of the head, and no additional supporting means is required. However, if the transducer happens to be positioned other than vertically with the working face 11 upwardly, some structure may be required to support the toroid in position. One such structure is illustrated in Fig. 2 as consisting of a wire framework resting on the flange 14 and against the rear side of the toroid 18. As shown, this framework consists of a circular base member 20 from which struts 21 extend parallel to the motion amplifier and are bent outwardly at their free ends, as indicated at 22, to bear against the toroid 18.

It will be noted that a portion of the toroid 18- is in direct contact with the head 16, so that only a thin film of liquid would exist between the toroid and the head at the area of contact, such film being too thin to have However, as previously indicated, the toroid prevents the generation of pressure waves at parts of the head that are spaced therefrom, in addition to those that are in contact. Thus, the overhanging surfaces 17 in Fig. 3 are sufficiently close to the toroid to prevent the generation of pressure waves of appreciable magnitude therein, the mass of water between the surface 17 and the toroid moving bodily to compress the air within the toroid in response to vibration of the surface 17.

surfaces at which pressure waves are effectively suppressed is a function of the length of the acoustic waves in the liquid medium at the frequency of vibration of the transducer. Appreciable reduction-in'pressure will be obtained if the distance is reduced below one-quarter wavelength, and it is usually possible in practice to reducethe distance to a much greater extent. Thus, with atransducer operating at 000 c.p.c-, in Water, the wavelength would be six inches, whereas the maximum distance between any portion of the rearwardly facing surface 17 and the toroid would not need to be in excess of .25 inch.

Fig. 4 shows a modification'of the pressure-release structure of Fig. in which the air-filled body, instead of being a true toroid, is in the form of a radially thin, axially elongated toroid extending the full distance from theflange 14 to the head16, so that it is inherently self-supportingon the transducer Without employing a separate supporting structure such as the Wire cage. of Fig. 2. The toroid may contain gas. at the-ambient pressure or at a higher pressure, since regardless of the gas pressure, within reasonable limits, the acoustic pressure is of an entirely different order of magnitude than that of a liquid. v

Futhermore, it is not essentiahthat the toroid be a hollow member as shown. It'may' be of solid cellular material, such as sponge rubber or the like, having a large number'of small air cavities withintit. However, the outer wall in each case should be impervious so that the gas contained therewithin will not leak out'in' service.

Of course, the toroid should be made of sufiiciently elastic material to permit its application by stretching it over the head of the transducer, so thattoroids can be applied or removed without removing the transducer from the tank. Alternatively, non-elastic toroids may be used by installing them on the transducer over the small end thereof prior to installation of the transducer in the tank wall.

v Although for the purpose of explaining the invention 'a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I donot desire to be limited to the exact details shown and described.

I claim:

1. In combination: a sonic transducer for generating sonic waves in a liquid and having yibratingworking and non-working faces immersed in said liquid; and pressurerelease means immersed in said liquid adjacent said nonworking face for reducing the effective acoustic coupling between said non-working face and said liquid; atleast a portion of said nonworking face being out of contact with said pressure-release means but spaced therefrom a distance substantially lessthan a half. wave-length of said sonic waves in said liquid.

2. Apparatus in accordance with claim 1 in which said pressure-release means is a hollow gas-containing body of acoustically yieldable material.

3. Apparatus according to claim 2 in which said transducer has a neck portion and a head portion projecting laterally beyond [the neck portion; and said hollow gascontaining body, is an endless tubular member encircling said neck with its forward surfacev adjacent said head.

4. Apparatus according to claim 3' in which said trans ducer is positioned with its head portion above said neck portion whereby said hollow gas-containing body is'reztaine'd adjacent said head portion by its buoyancy..

5. Apparatus according to claim Zincluding means, for engaging said gas-containing body and retaining it adjacent said rear face. v

6. Apparatus according to claim 3 in which said endless tubular member is axially elongate and radially thin,

and extends axially the full length of said neck portion of said transducer.

References Cited in the file ofthis patent- UNITED STATES- PATENTS 2,792,674 1 Balamuth May 21, 1957 

